Excellent question!   There are many different companies making IPLs now and they are not all created equally.  The ones sold to salons and medispas tend to be less powerful and therefore less effective.  And, some doctors don't know which laser companies are best or invest in inferior equipment in an effort to save on the price. 

If you are going to a clinic where you are getting excellent treatments,  you can't assume treatments elsewhere will be the same. The effectiveness is related to the equipment and the person operating it.  Even if you try to find a clinic closer to home with the same laser equipment, you can't be sure the person operating the laser is as experienced or capable.  My vote is to stay with the clinic with a proven track record of excellence.

 But, please call the clinic where you received the less effective treatment and let them know.  They may offer to redo it.     Hope this helps, Dr. I